Band-Gap Modulation in Single Bi³⁺-Doped Yttrium-Scandium-Niobium Vanadates for Color Tuning over the Whole Visible Spectrum

The use of rare-earth (RE) (e.g., Eu2+/Ce3+) ions as single luminescent centers in phosphors with tailorable emission properties has been extensively studied for their potential use in white LEDs. However, significant limitations remain, in particular, for red-emitting phosphors due to the inherently broad excitation bands which result from the underlying d-f transitions and span large parts of the visible spectral region. Guided by density functional theory calculations on the ligand structure of the non-RE Bi3+ion, we report here on an alternative class of phosphors, [(Y,Sc)(Nb,V)O4:Bi3+], which exhibit homogeneous Bi3+luminescence. In these materials, adjustment of the cation fractions enables dedicated tailoring of the excitation scheme within the spectral range of ∼340-420 nm and, in the meanwhile, allows for tunable emission spanning from about 450 nm (blue) to 647 nm (orange-red). The practical absence of any overlap between the emission and excitation spectra addresses the issues of emission color purity and visible reabsorption. Tailoring through band-gap modulation is achieved by single or parallel substitution of Nb by V and Y by Sc. Such topochemical design of the ligand configuration enables modulation of the electronic band gap and thus provides a new path toward tunable phosphors, exemplarily based on Bi3+single doping.